<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 
<html>
<head>
<title>Layout management in QtJambi</title>
<link rel="stylesheet" href="/cfg/format.css" type="text/css">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<meta name="keywords" content="GUI, layout management, QtJambi, Java">
<meta name="description" content="Layout management in QtJambi">
<meta name="language" content="en">
<meta name="author" content="Jan Bodnar">
<meta name="distribution" content="global">

<script type="text/javascript" src="/lib/jquery.js"></script>
<script type="text/javascript" src="/lib/common.js"></script>

</head>

<body>

<div class="container">

<div id="wide_ad" class="ltow">
<script type="text/javascript"><!--
google_ad_client = "pub-9706709751191532";
/* 160x600, August 2011 */
google_ad_slot = "2484182563";
google_ad_width = 160;
google_ad_height = 600;
//-->
</script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
</div>

<div class="content">

<a href="/" title="Home">Home</a>&nbsp;
<a href="..">Contents</a>


<h1>Layout management in QtJambi</h1>

<p>
In this part of the QtJambi programming tutorial, we will introduce layout managers. 
</p>

<div class="center"> 
<script type="text/javascript"><!--
google_ad_client = "pub-9706709751191532";
/* horizontal */
google_ad_slot = "1734478269";
google_ad_width = 468;
google_ad_height = 60;
//-->
</script> 
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> 
</script> 
</div> 

<p>
When we design the GUI of our application, we decide what 
components we will use and how we will organize those components
in the application. To organize our components, we use specialized
non visible objects called layout managers. There are several options in QtJambi.
We can use absolute positioning, built-in layout managers or create a custom layout
manager. We can also visually build the layouts using the Qt Designer. 
</p>

<p>
QtJambi has some important built-in layout managers. The <b class="keyword">QVBoxLayout</b> 
class lines up widgets vertically. <b class="keyword">QHBoxLayout</b> lines up widgets horizontally.
The <b class="keyword">QGridLayout</b> class lays out widgets in a grid. The grid layout is the most
flexible layout manager. The box layouts nest into one another to create complex layouts. 
</p>


<h2>Absolute positioning</h2>

<p>
In most cases, programmers should use layout managers. There are a 
few situations, where we can use absolute positioning. In absolute 
positioning, the programmer specifies the position and 
the size of each widget in pixels. The size and the position of a 
widget do not change, if you resize a window. Applications look different 
on various platforms, and what looks OK on Linux, might not look OK on Mac.
Changing fonts in your application might spoil the layout. If you 
translate your application into another language, you must redo your 
layout. For all these issues, use the absolute positioning only when you
have a reason to do so.
</p>

<pre class="code">
package com.zetcode;

import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QLabel;
import com.trolltech.qt.gui.QPixmap;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 *
 * In this program, we lay out widgets
 * using absolute positioning
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified April 2009
 */

public class JambiApp extends QWidget {
    
    public JambiApp() {
        
        setWindowTitle("Absolute");

        initUI();

        resize(300, 280);
        move(300, 300);
        show();
    }
    

    private void initUI() {

        setStyleSheet("QWidget { background-color: #414141 }");

        QPixmap bardejov = new QPixmap("bardejov.jpg");
        QPixmap rotunda = new QPixmap("rotunda.jpg");
        QPixmap mincol = new QPixmap("mincol.jpg");

        QLabel barLabel = new QLabel(this);
        barLabel.setPixmap(bardejov);
        barLabel.move(20, 20);

        QLabel rotLabel = new QLabel(this);
        rotLabel.setPixmap(rotunda);
        rotLabel.move(40, 160);

        QLabel minLabel = new QLabel(this);
        minLabel.setPixmap(mincol);
        minLabel.move(170, 50);
    }


    public static void main(String[] args) {
        QApplication.initialize(args);
        new JambiApp();
        QApplication.exec();
    }
}
</pre>

<p>
In this example, we show three images using the absolute positioning.
</p>

<pre class="explanation">
QLabel barLabel = new QLabel(this);
barLabel.setPixmap(bardejov);
</pre>

<p>
The <b class="keyword">QLabel</b> widget is used to hold the image. 
</p>

<pre class="explanation">
barLabel.move(20, 20);
</pre>

<p>
We use the <b class="keyword">move()</b> method to position the label on the
window at x=20, y=20. 
</p>

<p>
When we resize the window, the labels retain their initial size. 
</p>

<br>
<img src="/img/gui/qtjambi/absolute.png" alt="Absolute">
<div class="figure">Figure: Absolute positioning</div>


<h2>Buttons example</h2>

<p>
In the following example, we will position two buttons in the bottom right corner
of the window. 
</p>

<pre class="code">
package com.zetcode;

import com.trolltech.qt.core.Qt;
import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QHBoxLayout;
import com.trolltech.qt.gui.QPushButton;
import com.trolltech.qt.gui.QVBoxLayout;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 *
 * In this program, use box layouts
 * to position two buttons in the
 * bottom right corner of the window
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified April 2009
 */

public class JambiApp extends QWidget {
    
    public JambiApp() {
        setWindowTitle("Buttons");

        initUI();

        resize(300, 150);
        move(300, 300);
        show();
    }
    
    private void initUI() {

        QVBoxLayout vbox = new QVBoxLayout(this);
        QHBoxLayout hbox = new QHBoxLayout();

        QPushButton ok = new QPushButton("OK", this);
        QPushButton apply = new QPushButton("Apply", this);

        hbox.addWidget(ok, 1, Qt.AlignmentFlag.AlignRight);
        hbox.addWidget(apply);

        vbox.addStretch(1);
        vbox.addLayout(hbox);
    }
    
    public static void main(String[] args) {
        QApplication.initialize(args);
        new JambiApp();
        QApplication.exec();
    }
}

</pre>

<p>
We use nested box layouts to get our intended layout. 
</p>

<pre class="explanation">
QVBoxLayout vbox = new QVBoxLayout(this);
QHBoxLayout hbox = new QHBoxLayout();
</pre>

<p>
We use one vertical and one horizontal box. 
</p>

<pre class="explanation">
QPushButton ok = new QPushButton("OK", this);
QPushButton apply = new QPushButton("Apply", this);
</pre>

<p>
These are the two buttons, that will go into the bottom
right corner of the window. 
</p>

<pre class="explanation">
hbox.addWidget(ok, 1, Qt.AlignmentFlag.AlignRight);
</pre>

<p>
We put the ok button into the horizontal box. The second parameter
is the <b class="keyword">stretch</b> factor. It expands the area allotted to the
ok button. It takes all available space left. Inside this area, the button is aligned
to the right. 
</p>

<pre class="explanation">
vbox.addStretch(1);
</pre>

<p>
This line creates a vertically expanded white space, which will push the horizontal
box with the buttons to the bottom. 
</p>

<pre class="explanation">
vbox.addLayout(hbox);
</pre>

<p>
The horizontal box is nested into the vertical box. 
</p>

<br>
<img src="/img/gui/qtjambi/buttons.png" alt="Buttons example">
<div class="figure">Figure: Buttons example</div>


<h2>Windows example</h2>

<p>
The following is a more complicated example with nested box layouts.
</p>

<pre class="code">
package com.zetcode;

import com.trolltech.qt.core.Qt.AlignmentFlag;
import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QHBoxLayout;
import com.trolltech.qt.gui.QLabel;
import com.trolltech.qt.gui.QPushButton;
import com.trolltech.qt.gui.QTextEdit;
import com.trolltech.qt.gui.QVBoxLayout;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 *
 * In this program, use box layouts
 * to create a windows example
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified April 2009
 */

public class JambiApp extends QWidget {
    
    public JambiApp() {

        setWindowTitle("Windows");

        initUI();

        resize(350, 300);
        move(300, 300);
        show();        
    }

    private void initUI() {

        QVBoxLayout vbox = new QVBoxLayout(this);

        QVBoxLayout vbox1 = new QVBoxLayout();
        QHBoxLayout hbox1 = new QHBoxLayout();
        QHBoxLayout hbox2 = new QHBoxLayout();

        QLabel windLabel = new QLabel("Windows", this);
        QTextEdit edit = new QTextEdit(this);
        edit.setEnabled(false);

        QPushButton activate = new QPushButton("Activate", this);
        QPushButton close = new QPushButton("Close", this);
        QPushButton help = new QPushButton("Help", this);
        QPushButton ok = new QPushButton("OK", this);

        vbox.addWidget(windLabel);

        vbox1.addWidget(activate);
        vbox1.addWidget(close, 0, AlignmentFlag.AlignTop);
        hbox1.addWidget(edit);
        hbox1.addLayout(vbox1);

        vbox.addLayout(hbox1);

        hbox2.addWidget(help);
        hbox2.addStretch(1);
        hbox2.addWidget(ok);
        
        vbox.addLayout(hbox2, 1);

        setLayout(vbox);
    }
    
        
    public static void main(String[] args) {
        QApplication.initialize(args);
        new JambiApp();
        QApplication.exec();
    }
}
</pre>

<p>
In this layout, we use two vertical and horizontal boxes. 
</p>

<pre class="explanation">
QVBoxLayout vbox = new QVBoxLayout(this);
</pre>

<p>
This is the base layout of the example. 
</p>

<pre class="explanation">
vbox.addWidget(windLabel);
</pre>

<p>
First goes the label widget. It goes simply to the top of the
vertical box. 
</p>

<pre class="explanation">
vbox1.addWidget(activate);
vbox1.addWidget(close, 0, AlignmentFlag.AlignTop);
hbox1.addWidget(edit);
hbox1.addLayout(vbox1);

vbox.addLayout(hbox1);
</pre>

<p>
In the center part of the window we have a text edit widget and
two vertically lined up buttons. The buttons go into a vertical box. The
buttons are aligned to the top within this vertical box. The vertical box
and the text edit go into a horizontal box. This horizontal box goes to the base
vertical box, just below the label widget. 
</p>

<pre class="explanation">
hbox2.addWidget(help);
hbox2.addStretch(1);
hbox2.addWidget(ok);

vbox.addLayout(hbox2, 1);
</pre>

<p>
The help and the ok button go into another horizontal box. There is 
an expanded white space between these two buttons. Again, the horizontal box
goes to the base vertical box. 
</p>

<pre class="explanation">
setLayout(vbox);
</pre>

<p>
The base vertical box is set to be the main layout of the window. 
</p>

<br>
<img src="/img/gui/qtjambi/windows.png" alt="Windows example">
<div class="figure">Figure: Windows example</div>


<h2>New Folder example</h2>

<p>
In the last example, we use the <b class="keyword">QGridLayout</b> manager to 
create a New Folder layout example.  
</p>

<pre class="code">
package com.zetcode;

import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QGridLayout;
import com.trolltech.qt.gui.QLabel;
import com.trolltech.qt.gui.QLineEdit;
import com.trolltech.qt.gui.QPushButton;
import com.trolltech.qt.gui.QTextEdit;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 *
 * In this program, use the QGridLayout
 * to create a New Folder example
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified April 2009
 */

public class JambiApp extends QWidget {
    
    public JambiApp() {

        setWindowTitle("New Folder");

        initUI();

        move(300, 300);
        show();
    }

    private void initUI() {

        QGridLayout grid = new QGridLayout(this);

        QLabel nameLabel = new QLabel("Name", this);
        QLineEdit nameEdit = new QLineEdit(this);
        QTextEdit text = new QTextEdit(this);
        QPushButton okButton = new QPushButton("OK", this);
        QPushButton closeButton = new QPushButton("Close", this);

        grid.addWidget(nameLabel, 0, 0);
        grid.addWidget(nameEdit, 0, 1, 1, 3);
        grid.addWidget(text, 1, 0, 2, 4);
        grid.setColumnStretch(1, 1);
        grid.addWidget(okButton, 4, 2);
        grid.addWidget(closeButton, 4, 3);
    }
    
    public static void main(String[] args) {
        QApplication.initialize(args);
        new JambiApp();
        QApplication.exec();
    }
}
</pre>

<p>
In our example, we have one label, one line edit, one text edit and two buttons. 
</p>

<pre class="explanation">
QGridLayout grid = new QGridLayout(this);
</pre>

<p>
We create an instance of the <b class="keyword">QGridLayout</b> manager. 
</p>

<pre class="explanation">
grid.addWidget(nameLabel, 0, 0);
</pre>

<p>
We place the label widget in the first cell of the grid. The cells count from 0. 
The last two parameters are the row and column number. 
</p>

<pre class="explanation">
grid.addWidget(nameEdit, 0, 1, 1, 3);
</pre>

<p>
The line edit widget is placed at the first row, second column. 
The last two parameters are the row span and the column span. Horizontally, the
widget will span three columns. 
</p>

<pre class="explanation">
grid.setColumnStretch(1, 1);
</pre>

<p>
The parameters of the method are the column number and the stretch factor.
Here we set stretch factor 1 to the second column. This means, that this column will take
all remaining space. This was set, because we wanted our buttons to retain their initial size. 
</p>


<br>
<img src="/img/gui/qtjambi/newfolder.png" alt="New Folder example">
<div class="figure">Figure: New Folder example</div>

<hr class="btm">

<p>
In this part of the QtJambi tutorial, we mentioned layout management of widgets. 
</p>


<br>
<div class="center"> 
<script type="text/javascript"><!--
google_ad_client = "pub-9706709751191532";
/* horizontal */
google_ad_slot = "1734478269";
google_ad_width = 468;
google_ad_height = 60;
//-->
</script> 
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> 
</script> 
</div> 
<br>


<div class="botNav, center">
<span class="botNavItem"><a href="/">Home</a></span> ‡ <span class="botNavItem"><a href="..">Contents</a></span> ‡
<span class="botNavItem"><a href="#">Top of Page</a></span>
</div>


<div class="footer">
<div class="signature">
<a href="/">ZetCode</a> last modified April 29, 2009  <span class="copyright">&copy; 2007 - 2012 Jan Bodnar</span>
</div>
</div>

</div> <!-- content -->

</div> <!-- container -->

</body>
</html>


